Rotary transformer structure

ABSTRACT

An apparatus for coupling electrical energy between a stator and rotor member without physical contact between relatively moving current carrying members and without relative rotation of any magnetic structure comprises a rotor shaft on which is mounted a nonconductive, nonmagnetic rotor coil-supporting flange which extends between stationary magnetically permeable stator core halves. The stator core is provided with a stator coil for transmission of electrical signals between the rotatable rotor coil and the stationary stator coil. Alternatively, the magnetically permeable core halves can each be secured to the rotor shaft for rotation therewith, while a nonconductive nonmagnetic and stationary stator coil-supporting flange extends between such core halves from the apparatus housing.

United States Patent 2,432,982 12/1947 Braddon et al.

lnventor Douglas Maake Troy, Mich. Appl. No. 91,836 Filed Nov. 23, 1970 Patented Oct. 5,1971 Assignee Lebow Associates, Inc.

Troy, Mich.

ROTARY TRANSFORMER STRUCTURE 8 Clalms, 4 Drawlng Figs.

U.S. Cl 336/120, 336/ 123 Int. Cl H0lt2l/04 Field of Search 336/1 15, 117, 118,119,120, 122, 123

References Cited UNITED STATES PATENTS 3,317,873 5/1967 l-limmelstein et al. 336/120 3,348,181 10/1967 Stromswold... 336/120 3,531,749 9/1970 Treter et al. 336/120 Primary Examiner-Thomas J. Kozma Attorney-Cullen, Settle, Sloman 81. Cantor ABSTRACT: An apparatus for coupling electrical energy between a stator and rotor member without physical contact between relatively moving current carrying members and without relative rotation of any magnetic structure comprises a rotor shaft on which is mounted a nonconductive, nonmagnetic rotor coil-supporting flange which extends between stationary magnetically permeable stator core halves. The stator core is provided with a stator coil for transmission of electrical signals between the rotatable rotor coil and the stationary stator coil. Alternatively, the magnetically permeable core halves can each be secured to the rotor shaft for rotation therewith, while a nonconductive nonmagnetic and stationary stator coilsupporting flange extends between such core halves from the apparatus housing.

PATENTED um sum 1161 1; 230

58 INVENTOR.

DOUGLAS MAAKE.

CULLEN, SETTLE, SLOMAN 8 ATT 'YS.

CANTOR.

ROTARY TRANSFORMER STRUCTURE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to rotary transformers, which have recently found widespread applications in such fields as electronic measurements, nondestructive testing, monitoring and supplying electrical energy to a rotatable member. The use of conventional slipring assemblies in such applications is often undesirable, since their inherent high friction characteristics cause excessive wear and increased maintenance, and also introduce the danger of short circuits from the accumulation of electrically conductive particles between the sliprings. In addition, conventional slipring assemblies have a sparking characteristic, making them unsuitable for explosive environments.

Rotary transformers eliminate many of the above disadvantages, since they transmit electrical signals between rotating and stationary members without any physical contact such as by brushes, fluid couplings or the like. Rotary transformers generally comprise a rotating magnetic structure and coil and a stationary magnetic structure and coil. A suitable airgap must be maintained between the rotating and stationary members. Since physical contact between relatively moving members is eliminated, friction induced wear and heating are eliminated, as is the danger of arcing. Signal transfer is generally unaffected by the presence of oil, water or other environmentals contaminants.

In conventional rotary transformers, the airgap between the rotating and stationary magnetic cores is extremely critical, since its width and area affects the reluctance of the transformer. Since a narrow gap enhances transformer perfonnance, close manufacturing tolerances on the shaft, bearings and so forth are essential to maintain a constant and minimum gap. Hence, optimum reliability and performance requires costly precision and control.

Dimensional changes in the airgap, caused by relative rotational or axial or radial motions or thermal growths between stator and rotor, change the magnetic transfer characteristics of the transformer, which in turn directly affect the coefficient of coupling, mutual inductance and efficiency (Q) of the transformer.

Accordingly, the primary object of the present invention is to provide an improved rotary transformer which effectively and economically overcomes the above-mentioned shortcomings of conventional rotary transformers.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate preferred embodiments of the present invention in which:

FIG. 1 is a sectional side elevation of a first embodiment of the present improved rotary transformer, having a radial flange type of support for the rotor coil, and an axial airgap;

FIG. 2 is an end view of the structure shown in FIG. 1, as seen in the direction of the arrows 2-2;

FIG. 3 is a partial enlarged cross section illustrating the structure of FIG. 1 in greater detail; and

FIG. 4 is an enlarged partial cross section of a second embodiment, illustrating a tubular type of support for the rotor coil and a radial airgap.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 to 3, the improved rotary transformer, generally indicated at 10, comprises a rotor shaft 12 conventionally supported for rotation in aligned bearings (not shown) mounted in a transformer housing (not shown) of any desired construction. A radial flange or disc 14 is secured to rotor shaft 12 for rotation therewith, and is provided with an annular member 16 which is U-shaped in cross section for the support of a rotor coil 18. Flange 14 and rotor coil-supporting member 16 are made of a nonconducting and nonmagnetic material, preferably of a fiber glass nature, to prevent any electrical or magnetic influences on the performance of the transformer.

Rotor coil 18 is suitably provided with electrical leads 20 for connection to an appropriate rotating current generating or using device, depending upon the desired application. Leads 20 are preferably embedded within a radial recess in flange 14 for protection of the leads and to maintain the wall thickness of flange 14 at a desired minimum. Leads 20 may extend axially along grooves 13 in shaft I2, or they may extend through the interior of a tubular shaft if desired.

Rotor coil 18 together with its support 16 and flange 14 extend into a stationary stator assembly, generally indicated at 22, which is comprised of a magnetically permeable core assembly 24 of generally U-shaped configuration providing opposite parallel side legs 26 and 27 connected by a bridge portion 28 which extends across rotor coil 18. Side legs 26 and 27 of stator core member 24 extend toward shaft 12 along both sides of rotor coil support 16 and flange I4, and connect to torroidal stator core members 42 and 44 which concentrically surround shaft 12. Stator core members 42 and 44 are axially spaced from each other to provide an axial airgap 32 through which rotor coil support disc 14 extends.

Bridge portion 28 of stator core 24 supports a stator coil 30 which is outwardly spaced from rotor coil 18. Stator coil 30 is suitably connected by leads 40 to an appropriate nonrotating electrical device, depending upon the desired application. Thus, when the transformer is energized, electrical signals are inductively linked between coils 14 and 30 by means of the magnetic circuit consisting of stator 24 and airgap 32.

Thus, in contrast to conventional practice, there is no rotor core. The entire core structure is stationary and functions as one integral unit. As shown, stator core assembly 24 com prises three separate members, but for ease of manufacturing it may comprise additional members pieced together to form the shape shown without any substantial increase in magnetic reluctance. All of the magnetic cores are made from conventional magnetic material, such as ferrite.

The airgap 32 between stator core members 42 and 44 is of a predetermined fixed dimension sufficient to prevent frictional contact between rotating disc 14 and the inner opposed surfaces of members 42 and 44. The resultant magnetic reluctance across gap 32 is minimized by the large surface areas of stator core members 44 and 42, and is directly proportional to the width of the gap between the opposed inner surfaces of these members.

The magnetic reluctance across gap 32 remains constant at all times, permitting axial or radial play or misalignment of rotor shaft 12. Thus, regardless of the relative position of disc 14 within gap 32, the net magnetic reluctance across the gap remains unaffected. This configuration is an improvement over conventional rotary transformers in which the rotor core rotates relative to the stator core, requiring airgaps on both sides of the rotor core, with resultant proportional change in reluctance across the two airgaps with axial or radial play.

Referring to the alternative embodiment in FIG. 4, rotor shaft 12a carries a cylindrical or tubular member 46 which is connected to shaft 12 for rotation therewith by flange 48. The free end of tube 46 is formed with outwardly extending flanges 50 and 52 to form a channel-shaped support for a rotor coil 54 wound around the free end of tube 46. Rotor coil 54 is suitably electrically connected to an appropriate electrical device by means of leads 56 and 58 which extend through the inside of tube 46 and out through an aperture in end flange 48.

The nonconductive and nonmagnetic rotor coil-supporting tube 46 extends into a Ushaped stator core assembly 60, which has parallel legs 62 and 64 disposed coaxially with rotor shaft 120. A stator coil assembly 66 is wound around outer leg 62 of stator core 60 and is outwardly spaced from rotor coil 54. The stator coil 66 is suitably electrically connected to an appropriate electrical device by leads 70 and 72.

In addition to the U-shaped portion of stator core assembly 60, the stator core further comprises a pair of radially spaced concentric torroidal members 74 ad 76 secured to shortened leg 64 and the inner surface of outer leg 62, respectively.

A radial airgap 68 between the stationary and radially spaced stator core sections 74 and 76 provides clearance for rotating tube 46. Since gap 68 is between two stationary members, its width and the magnetic reluctance necessarily remain constant, irrespective of the tolerances on the rotating elements. With the exception of the radial rather than axial airgap configuration of FIG. 4, this embodiment functions'in the same manner as the embodiment of FIGS. 1-3 described above. The radial airgap embodiment of FIG. 4 is of particular advantage in rotary transformers having to accommodate relatively large axial end play of the rotor shaft 120.

Further stator core variations of the illustrated embodiments could take the cross-sectional form illustrated in either FIG. 3 or FIG. 4, but with the entire stator core members being a complete annulus or torroid, rather than merely portions 42, 44 or 74, 76. In such arrangements the stator coil could be wound around the full inner surface of annular portion 28 of FIG. 3 or annular portion 62 of FIG. 4, so as to be concentric with rotor coil 18 or 54, respectively.

As a further alternative, relative motion between magnetic core members can be eliminated by securing the entire magnetic core structure to the rotor shaft for rotation therewith. This can be accomplished with either the radial or the axial airgap constructions described above. AS will be understood by those skilled in the art, this would involve a simple reversal of parts, with the rotor coil-supporting flanges of the illustrated constructions becoming stator coil supporting flanges, and such flanges extending through appropriately positioned airgaps between the rotor core halves to a mounting point or the transformer housing.

Hence, the improved rotary transformers of this invention eliminate relative rotation of the magnetic core members. In both the radial and axial gap embodiments, whether the magnetic structure is fully stationary or fully rotational, the gap is between relatively nonrotating members, and therefore remains constant and can be minimized since it is unaffected by rotation of any part of the transformer. Reluctance is therefore also constant, and the various sources of signal distortion described above are eliminated.

While the foregoing description discloses specific detailed embodiments of the invention for the purpose of illustration, many changes could be made in the construction and arrangement without departing from the spirit and essential characteristic of the invention. Therefore, these embodiments are to be considered as illustrative only and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description.

1. A rotary transformer comprising: a rotor shaft; a nonconductive nonmagnetic rotor coil support means coaxially fixed on said rotor shaft for rotation therewith and carrying a rotating coaxial rotor coil; a nonrotatable magnetically permeable stator core member disposed adjacent said shaft in spaced relation thereto and partly enclosing a portion of said rotor coil support means and said rotor coil; said stator core member having a stator coil supported thereon adjacent to but spaced from said rotor coil; said nonrotatable stator core member including a pair of magnetically permeable torroidal core sections coaxially surrounding said rotor shaft, said torroidal core sections being disposed relative to each other to form a gap between them for the extension of said nonconductive rotor coil support therethrough in nonabutting relationfixed gap dimension uneffected by a relative misaligned posiport means comprising a radial flange provided at its outer circumference wit a c annel-shape portion surrounding and spaced outwardly from said torroidal core sections for the receipt and retainment of said rotor coil.

4. In the rotary transformer of claim 1, said pair of torroidal core sections being coplanar and radially spaced from each other, said nonconductive rotor coil support means extending axially through the radial gap between said torroidal core sections.

5. In the rotary transformer of claim 4, said rotor coil support means comprising a tubular member coaxially surrounding said rotor shaft and having one end fixed to said shaft axially beyond said stator core member; the free end of said tubular member extending into said stator core member and being provided with a circumferential channel-shaped portion for the support of said rotor coil.

6. In the rotary transformer of claim 5, said stator core member being substantially U-shaped with its parallel legs extending axially on opposite radial sides of said tubular rotor coil-supporting member, and said coaxial and coplanar torroidal core sections being mounted on he respective ends of said stator core legs, said tubular rotor coil-supporting member extending axially through the radial gap between said torroidal core sections.

7. An inductive coupling between relatively fixed and rotatable members comprising: a rotor shaft, a nonconductive rotor coil support member fixedly mounted on said rotor shaft for rotation therewith; a nonrotatable magnetically permeable stator core member disposed adjacent said rotor shaft; a pair of magnetically permeable torroidal core members coaxially surrounding said rotor shaft and fixedly secured to said stator core member to form a unitary structure therewith; said torroidal core members being spaced from each other to permit the extension of said rotatable nonconductive rotor coil support member therethrough; said rotor coil support member carrying a rotor coil and said stator core member carrying a stator coil radially spaced from said rotor coil.

8. A rotary transformer comprising: a housing: a rotor shaft rotatably mounted in said housing; a nonconductive nonmagnetic coil support means coaxially fixed on one of said rotor shaft and said housing and carrying a first coaxial coil; a mag netically permeable core member fixed on the other of said rotor shaft and said housing and partly enclosing a portion of said coil support means and said first coil; said core member having a second coil supported thereon adjacent to but spaced from said first coil; said core member including a pair of magnetically permeable core sections disposed relative to each other to form a gap between them for the extension of said nonconductive coil support means therethrough in nonabutting relationship; said gap between said core sections providing a constant gap dimension uneffected by any relative rotation between said core sections. 

1. A rotary transformer comprising: a rotor shaft; a nonconductive nonmagnetic rotor coil support means coaxially fixed on said rotor shaft for rotation therewith and carrying a rotating coaxial rotor coil; a nonrotatable magnetically permeable stator core member disposed adjacent said shaft in spaced relation thereto and partly enclosing a portion of said rotor coil support means and said rotor coil; said stator core member having a stator coil supported thereon adjacent to but spaced from said rotor coil; said nonrotatable stator core member including a pair of magnetically permeable torroidal core sections coaxially surrounding said rotor shaft, said torroidal core sections being disposed relative to each other to form a gap between them for the extension of said nonconductive rotor coil support therethrough in nonabutting relationship; said gap between said torroidal core sections providing a fixed gap dimension uneffected by a relative misaligned position of said rotor shaft and said rotor coil support member.
 2. In the rotary transformer of claim 1, said stator core member being substantially U-shaped providing parallel spaced radially extending legs for extension along opposite sides of said rotor coil support means; said pair of torroidal core sections being axially spaced and fixedly mounted to opposite inner surfaces of said stator core member legs, said rotor coil support means extending radially through the axial gap between said torroidal core sections.
 3. In the rotary transformer of claim 2, said rotor coil support means comprising a radial flange provided at its outer circumference with a channel-shaped portion surrounding and spaced outwardly from said torroidal core sections for the receipt and retainment of said rotor coil.
 4. In the rotary transformer of claim 1, said pair of torroidal core sections being coplanar and radially spaced from each other, said nonconductive rotor coil support means extending axially through the radial gap between said torroidal core sections.
 5. In the rotary transformer of claim 4, said rotor coil support means comprising a tubular member coaxially surrounding said rotor shaft and having one end fixed to said shaft axially beyond said stator core member; the free end of said tubular member extending into said stator core member and being provided with a circumferential channel-shaped portion for the support of said rotor coil.
 6. In the rotary transformer of claim 5, said stator core member being substantially U-shaped with its parallel legs extending axially on opposite radial sides of said tubular rotor coil-supporting member, and said coaxial and coplanar torroidal core sections being mounted on he respective ends of said stator core legs, said tubular rotor coil-supporting member extending axially through the radial gap between said torroidal core sections.
 7. An inductive coupling between relatively fixed and rotatable members comprising: a rotor shaft, a nonconductive rotor coil support member fixedly mounted on said rotor shaft for rotation therewith; a nonrotatable magnetically permeable stator core member disposed adjacent said rotor shaft; a pair of magnetically permeable torroidal core members coaxially surrounding said rotor shaft and fixedly secured to said stator core member to form a unitary structure therewith; said torroidal core members being spaced from each other to permit the extension of said rotatable nonconductive rotor coil support member therethrough; said rotor coil support member carrying a rotor coil and said stator core member carrying a stator coil radially spaced from said rotor coil.
 8. A rotary transformer comprising: a housing: a rotor shaft rotatably mounted in said housing; a nonconductive nonmagnetic coIl support means coaxially fixed on one of said rotor shaft and said housing and carrying a first coaxial coil; a magnetically permeable core member fixed on the other of said rotor shaft and said housing and partly enclosing a portion of said coil support means and said first coil; said core member having a second coil supported thereon adjacent to but spaced from said first coil; said core member including a pair of magnetically permeable core sections disposed relative to each other to form a gap between them for the extension of said nonconductive coil support means therethrough in nonabutting relationship; said gap between said core sections providing a constant gap dimension uneffected by any relative rotation between said core sections. 